The subject of the present invention is a magnetic recording device, in particular for a storage means such as a hard disk and its fabrication process.
Perpendicular magnetic recording for which the memory points are recorded in a medium with off-plane magnetization has been identified as a very promising procedure for increasing storage densities (towards ultra-high storage densities) in computer hard disks. This technology has recently been instituted and marketed by the main industrial players in the sector: Seagate, Hitachi, Toshiba, etc.
Various solutions have been envisaged for solving the problem of superparamagnetic instability and attaining ultra-high storage densities, for example 1 Tbit per square inch, i.e. 0.155 Tbits per cm2, this corresponding to a 25 nm×25 nm memory point.
One of the most promising solutions is the implementation of so-called structured supports or “media” which allow inter alia a physical separation between the memory points.
This solution nevertheless exhibits troublesome limitations, one of the most significant of which is the wide distribution of the inversion fields of the various points, which is due in particular to the step of structuring the magnetic layer.
The main limitation is the presence of a wide distribution of the inversion fields which is observed by numerous groups and was reported on during the last Intermag/MMM conference in 2007. This wide distribution makes it problematic to apply these media to information storage, see in particular “Patterned media for future magnetic data storage”, by B. D. Terris, T. Thomson and G. Hu, Microsyst. Tech. 13, pages 189-196 2007.
When a layer is structured into dots, the coercive field of the dots becomes larger than that of the continuous layer and may even be very greatly increased. This has for example been observed in the article “Enhanced Coercivity in Submicrometer-Sized Ultrathin Epitaxial Dots with In-Plane Magnetization” by O Fruchart, J-F. Nozières, W. Wernsdorfer, D. Givord, F. Rousseaux and D. Decanini, Physical Review Letters 82, 1305, 1999.
For Co/Pt multilayers deposited to form a continuous support or medium, the coercive field is 170 Oe although it becomes greater than 1000 Oe when they are deposited to form a medium structured as dots 400 nm by 400 nm, see for example “Magnetic properties of Co/Pt multilayers deposited on silicon dot arrays”, by S. Landis, B. Rodmacq and B. Dieny, Physical Review B 6212271 2000. In this configuration, the structured dot represents the memory point itself and a consequence of this structuring may be that the inversion field of these dots may become very large and even sometimes greater than the field at saturation of the write pole pieces rendering the use of these media problematic.
Another difficulty with structured media or supports is the fact that the write/read head no longer sees a smooth continuous medium but a succession of depressions and dots which may impede its flight. This limitation is less significant than that previously presented in the sense that solutions may be devised such as that consisting for example in filling the space between the dots with a nonmagnetic material.
The defects induced by the structuring of the media itself which correspond inter alia to geometric inhomogeneities are very difficult to control especially when the size of the memory points becomes increasingly small when moving towards ultra-high storage densities.